We have used the Galileo G1, G2, G7, and G8 images to study the morpholo-
gy and degradation of impact craters on Ganymede. Results from the G1
and G2 data showed three types of degradation states: pristine, partially
degraded, and heavily degraded. With the more recent G7 and G8 images,
there are now several other distinct crater morphologies that we have
identified. Enki Catena is about 120 km in length and consists of 13
attached impact craters. The six craters in the chain that impacted onto
the bright terrain have visible bright ejecta while those that impacted
onto the dark terrain have barely visible ejecta. Kittu crater is about
15 km in diameter and it has a bright central peak surrounded by a bright
floor and hummocky wall material. The crater rim in the north is linear
in appearance at the location that corresponds to the boundary between
the groove terrain and the adjacent dark terrain, indicating structural
control by the underlying topography. The dark rays that are easily seen
in the Voyager images are barely visible in the Galileo image. Neith
crater has a central fractured dome surrounded by a jagged central ring,
smoother outer ejecta facies, and less prominent outer rings. Achelous
crater and its neighbor, which were imaged at low sun angle to show
topography, have smooth floors and subdued pedestal ejecta. Nicholson
Regio has tectonically disrupted craters on the groove and fractured
terrains while the surrounding smoother dark terrain has numerous degrad-
ed craters that may indicate burial by resurfacing or by regolith
development.